As I stated, I am not positive about the fenders/grille/etc. As to the bumper aspect, that has been discussed quite a lot on this and other forums in terms of how to get the bumpers tight to the body. I went through this on my 73, however in my case I was using 72 bumpers which forced me to use 72 brackets, however I still had to modify them a significant amount to get them in tight.
In your case, I believe the if you want the 70/71 look you need those bumpers and the corresponding brackets. Again not positive on the differences between 70/71 brackets and bumpers but I know 72 is different as are 73/74.
I am sure someone will chime is with more accurate information on this.